Extended Abstract (508K)4B.7
Vertical Transport of momentum within and surrounding isolated cumulus clouds
Paul B. Bogner, University of Hawaii at Manoa, Honolulu, HI; and G. M. Barnes
Numerical models indicate that the inclusion of shallow convection can increase the accuracy of simulated mean tropical circulations. However, model convection is based on conceptual and theoretical models often developed without the aid of detailed observations. Since cumulus clouds exist in large fields over the tropical oceans and land, it is vital to understand how these small clouds transport momentum and what effects they have on the environmental wind profile. Currently, there is no observational study of how vertical momentum transports evolve in cumulus clouds.
The rapid growth and decay of a cumulus cloud makes detailed sampling of cloud structures challenging. Consequently, studies describing aspects of cumulus life cycles are limited to several passes at one set altitude or one pass each at varying altitudes. The Convection and Precipitation/Electrification Experiment (CaPE), conducted during the summer of 1991 near Cape Canaveral, Florida, offers the opportunity to probe clouds with two highly maneuverable, well-equipped King Air aircraft both of which execute coordinated patterns for a nearly simultaneous penetration of a cloud at different altitudes. This allows for a detailed analysis of the vertical momentum fluxes within and surrounding the cloud as the clouds evolve.
We are studying a subset of 14 clouds that occurred from July 18 to August 10 of 1991 encompassing 149 aircraft passes. An upper- air sounding network of 10 stations as well as a 47 station automated surface mesonet network support the aircraft data and aid in determining the environmental stability and surface forcing within the region of cloud development. Plots of liquid water content, vertical velocity and the u and v components of wind speed are analyzed for each aircraft pass. We will present trends in the vertical transport of momentum as a function of cloud lifecycle along with comparisons between the aircraft levels. A relationship between mass flux and momentum flux will be explored. Findings will be discussed in light of the previous work on various conceptual models of cloud growth and mixing.
We will address the following issues: 1) How will the observed cloud momentum transports act to alter the environmental wind profile? 2) Do updrafts (downdrafts) transport higher (lower) momentum air preferentially? 3) How do transports vary with height in cloud? 4) Do the observed transports support or refute any of the conceptual models for cumulus development and does this point to a better parameterization?
Session 4B, Convection III (Parallel with Sessions 4A, 4C, & 4D)
Tuesday, 30 April 2002, 8:30 AM-10:30 AM
Previous paper Next paper